Forget everything your therapist told you and focus on your CV: A new study says that paycheck rules your state of mind.

The secret to a happy life is about as elusive as a solid definition of happiness itself. As with US Justice Potter Stewart's definition of obscenity ("I'll know it when I see it.") happiness is probably best understood when experienced.

A paper published on Tuesday in the Proceedings of the National Academy of Sciences does not bother with the ephemeral nature of things such as patience, meditation and having a good relationship with your family.

Happiness, and its more holistic cousin, well-being, can be understood in numbers.

For example, one previous study indicated that those with long daily commutes are less satisfied with their lives (of course they are -- they're spending most of it in traffic).

Another study on happiness carries bad news for men shorter than 1.78 meters or a female shorter than 1.62 meters. Yes, your taller friends are happier than you.

But the AP news agency reports that the new study says that it is all about cash -- roughly $75,000 annually, to be precise. Although earning more never hurts.

Those who earn less suffer from a decreased sense of well-being and happiness.

Angus Deaton, an economist at the Center for Healfth and Wellbeing at Princeton University told that AP that a salary of less than $75,000 means that, "Stuff is so in your face it's hard to be happy. It interferes with your enjoyment.''

Deaton, who co-authored the paper on height, and Daniel Kahneman reviewed surveys of 450,000 Americans conducted in 2008 and 2009 for the Gallup-Healthways Well-Being Index that included questions on people's day-to-day happiness and their overall life satisfaction.

Of course, it should be made clear that this is a US study, and that in many countries, a far lower sum would bring an equal measure of financial security.

Happiness got better as income rose but the effect levelled out at $75,000, Deaton said. On the other hand, their overall sense of success or well-being continued to rise as their earnings grew beyond that point.

You might want to make sure your boss does not read what Deaton says next.

"Giving people more income beyond 75K is not going to do much for their daily mood...but it is going to make them feel they have a better life" said Deaton.

Not surprisingly, someone who moves from a $100,000-a-year job to one paying $200,000 realises an improved sense of success. That does not necessarily mean they are happier day to day, Deaton said. Hopefully, that pay raise won't come with a longer commute.

The results were similar for other measures. For example, you probably will not be surprised to learn that researchers found that people were really happier on weekends, but that their deeper sense of well-being did not change.

Kahneman, a Nobel Prize winning psychologist, and Deaton undertook the study to learn more about economic growth and policy.

Some have questioned the value of growth to individuals, and Deaton said they were far from definitively resolving that question. But he added, "Working on this paper has brought me a lot of emotional well-being. As an economist I tend to think money is good for you, and am pleased to find some evidence for that.''

Overall, the researchers said, "as in other studies of well-being, we found that most people were quite happy and satisfied with their lives."